Bottles are frequently used to transport a fluid for later use or consumption. While the fluid remains in the bottle, it is often desirable or even necessary to maintain the fluid at or near a desired temperature. Additionally, it may be desirable to keep the fluid initially at one temperature and then raise the fluid to a higher temperature before use or consumption. For example, if baby milk or formula stored in a bottle is to be brought on an outing, such as a picnic, it may be desirable that the bottle be kept cool to inhibit bacteria formation and/or growth, and then warmed to a desired temperature prior to consumption by the baby.
Various devices have been proposed for at least partially achieving this objective. For example, U.S. Pat. No. 1,669,061 discloses an insulated wrap for baby bottles. Such a wrap, however, only serves to passively resist changes in temperature. On the other hand, U.S. Pat. Nos. 3,804,076, 4,838,242, and 6,234,165 disclose devices in which an active heating effect can be produced by thermal elements. However, these devices require elaborate, often bulky structures and sometimes utilize potentially toxic and/or messy thermal elements.